1. Field of the Invention
The present invention relates to a device and the use thereof for producing highly porous crystalline surface coatings and to a method using the device concerned.
2. Discussion of Background Information
Metal-organic frameworks (MOFs) are hybrid inorganic-organic solids with high porosity. Among their outstanding properties are high gas storage capacities for hydrogen and hydrocarbons and application potentials in the areas of gas separation, sensor technology and catalysis (Mueller, U.; Schubert, M.; Teich, F.; Puetter, H.; Schierle-Arndt, K.; Pastre, J. J. Mater. Chem. 2006, 16, 626-636).
Metal-organic frameworks are complex 2D or 3D zeolite-like networks with perfect translation symmetry. On the basis of coordination chemistry of the Werner type, metal-organic frameworks consist of metal cations Nm+ (m=2;3) and oligo-functionalized organic ligands. The design and precise control of the formation of the respective networks has been described and investigated repeatedly in the literature (G. Ferey, Chem. Soc. Rev. 2008, 37, 191, O. M. Yaghi, M O'Keeffe, N. W. Ockwig, H. K. Chae, M. Eddaoudi and J. Kim, Nature, 2003, 423, 705, K. Uemura, R. Matsuda and S. Kitagawa, J. Solid State Chem., 2005, 178, 2420-2429).
While the production of powdered metal-organic frameworks for storage materials can be carried out on a semi-industrial scale, the corresponding methods are not yet sufficient for nanotechnology. Such methods are required in particular for the production of membranes, catalytic coatings, chemical sensors and other nanotechnological applications.
For numerous applications of the coating of substrates with MOFs, in principle three possibilities have so far been pursued:                a) growth or direct deposition from solvothermal solutions        b) bringing together on surfaces nanocrystals previously formed in solution and        c) layer-by-layer (quasi epitaxial) growth on a surface. (Zacher, D.; Shekhah, O.; Wöll, C.; Fischer, R. A. Chem. Soc. Rev. 2009, 38, 1418-1429; Shekhah, O.; Materials, 2010, 3, 1302-1315)        
The production of metal-organic frameworks is usually performed by solvothermal or hydrothermal methods, in which crystalline MOF particles are precipitated from a mixture of the precursor substances. However, such powdered materials are not suitable for a series of applications.
The production of multilayer surface coatings from different substances is partially carried out by cyclical dipping of the substrate into reservoirs filled with dissolved substances. An example is the method for producing polyelectrolyte layers (Gero Decher, et al., Science 1997 277, 1232-1237).
In the case of this method, the approximately monomolecular formation of the layers with simultaneous bonding of the different layers one on top of the other results from the use of oppositely charged polyelectrolytes. After the formation of a monomolecular layer, an electrostatic repulsion occurs, and then the adsorption of further molecules of the same charge is inhibited. If, however, the substrate is subsequently dipped into a second reservoir with a charge opposite to that of the polyelectrolytes, there is an electrostatic bonding attachment of a monolayer of this substance. A cyclical alternation of the dipping into the two reservoirs has the effect that a defined stratification of the polyelectrolyte layers forms. The arrangement of the polyelectrolyte molecules within a layer does not have a crystalline character.
Apart from the deposition of such polyelectrolyte layers from solutions, there is also the production of multilayer coatings using spraying processes. Examples are the production of surface coatings or films by cyclical, alternating spraying on of poly(styrene sulfonate) and polydiallyl-dimethyl-ammonium solutions (Schlenoff J.; Dubas S.; and Farhat T.; Langmuir 2000; 16; 9968-9969).
The spraying process is in this case performed by means of simple, manually pumped spray bottles. The resultant films display a uniform surface and, because of the use of the layer-by-layer technique, have a layer structure with layers oriented perpendicularly to the surface (Izquierdo A.; Ono S. S., Voegel J. C.; Schaaf P. and Decher G.; Langmuir 2005; 21, 7558-7567; Kolasinska M. et al.; Langmuir 2009; 25, 1224-1232; Lu C. and Fery A. Chem. Mater. 2006; 18, 6204-6210).
Also known is an automated spraying process for generating polyelectrolyte layers applied by the layer-by-layer technique. The spraying process is in this case performed by way of three externally controlled solenoid valves and spray nozzles, which spray the polyelectrolytes or water as a rinsing medium sequentially onto a surface. The solenoid valves in this case allow the spraying of the media that are under pressure in storage vessels to be electronically switched on and off. The pressure in the storage vessels is maintained by way of a nitrogen supply line and manually adjustable pressure regulators. For producing the layers, polyelectrolytes, combinations of polyelectrolytes with nanoparticles and a combination of polyacrylic acid and polyethylene oxide, which act by way of hydrogen bridge bonds, were in turn used. However, none of these systems has crystalline orders that can be demonstrated by X-ray diffractometry.